The Insights are like that too. They use a dc to dc device that uses the hybrid battery as a source for power. You can easily use up the power by using both defrosters.
Also a low or bad starter battery can cause you to see little to no assist and mostly regen as it tries to charge the battery up. Many i2 users have gone to a larger group 51 battery and notice way more assist than before.
Also when you do regen braking it also turns on the dc to dc converter. So, the more braking you do the more it tops off the battery vs it falling before 12.5 volts among other varibles it watches.
Some people go as far as to precharge the 12 volt battery before their trip to help get a boost in mpg. I did that before I purchased my plug in kit. I notice a boost in trips for the first 7-12 miles or so.